Giuliano Ferrara speaks during the demostration in favour of former prime minister Silvio Berlusconi in Rome last month. Photograph: Fulvio Dalfelli/Demotix/Corbis

The Italian parliament was at a standstill on Wednesday after the country's main leftwing party joined Silvio Berlusconi's followers in voting for a suspension.

The vote was in protest at a decision by the supreme court aimed at preventing the media tycoon from evading a four-year jail sentence on a technicality.

The Democratic Party (PD) dropped its earlier opposition to a stoppage after its coalition partner, Berlusconi's Freedom People movement (PdL), scaled back its demands. The PdL initially called for a three-day strike, but agreed to settle for just oneday, ostensibly so its parliamentarians could hold a meeting.

There was uproar in parliament when the PD's spokesman announced the move, intended to preserve the unity of Enrico Letta's fragile left-right coalition.

The statement met with a barrage of whistling and booing from the internet-based Five Star Movement (M5S) and the radical Left Ecology Freedom party.

Speaking before the PD's U-turn, the M5S leader, Beppe Grillo, said: "We are no longer a parliamentary republic and perhaps we are no longer a democracy."

Roberto Maroni, the leader of the Northern League, which was in coalition with the PdL until 2011, called the suspension of parliament an "affront to democracy".

Berlusconi has already been convicted in two lower courts of a €7.5m (£6.5m) tax fraud orchestrated by his Mediaset TV company. The judges added a ban on Berlusconi holding office for five years, which would be an even harsher blow on top of the prison sentence, which he is unlikely to have to serve, which would be an even harsher blow.

If his case had followed its normal course through the supreme court, his final appeal would have been heard in about six months. But by then – as the result of a law passed by Berlusconi's government in 2005 – one of the counts on which he was charged would have been ruled out by a statute of limitations.

The judges would probably have had to send the case back to a lower court for a recalculation of the sentence. In Italy that could easily take 12 months, during which period the other count would have been timed out.

The supreme court decided Berlusconi's appeal should be heard on 30 July before a tribunal that deals with urgent matters during the summer legal holidays.

The billionaire politician's followers expressed outrage at the decision. The transport minister, Maurizio Lupi, said: "Millions of Italians wait years for justice, but for Silvio Berlusconi the [supreme court] gets convened in record time."

But the Corriere della Sera, the paper that first reported the loophole through which the leader of the Italian right might have wriggled, pointed to a 1969 law that instructs judges to speed up cases that are at risk of lapsing during the summer break because of a statute of limitations.